1. Technical Field
The present invention relates to methods for manufacturing light-emitting diodes and in particular to a method for producing high efficiency light-emitting diodes.
2. Description of the Related Art
Nitride semiconductor light emitting devices have been employed in a wide variety of applications, including traffic lights, backlights of electronic apparatus, outdoor optical displays, white light illumination apparatus, UV light apparatus, and data storage apparatus.
In a nitride semiconductor light-emitting device, a structure of the nitride semiconductor light-emitting device includes a substrate, which can be made of sapphire or SiC (silicon carbide). In a process of the nitride semiconductor light-emitting device manufacture, the process includes forming an epitaxial light emitting stack on a substrate wafer, and then cutting the wafer into dice. The wafer can be separated into dice by a number of ways, for example, the wafer can be mechanically scribed, such as with a diamond scribe, and then be separated along scribing lines. However, the hardness of the sapphire or the SiC is greater than traditional III-V materials (for example, Si or GaAs), and it is difficult and time-consuming to cut the wafer made of sapphire or SiC. Furthermore, the consumption of the diamond is so great that the manufacturing cost is raised.
Another separation method involves scribing the wafer by a high energy density laser beam ablating the bonds between atoms of the substrate. In laser ablation scribing, the scribing temperature has to be high enough to break the crystal bonds of the substrate and then results in the build-up of waste material along the scribing lines. Because the light emitting from the light-emitting device can be absorbed by the waste material, the light extraction efficiency is reduced.
In U.S. Pat. No. 5,631,190, a dry etching method of removing by-products generated from cutting the silicon carbide substrate by the laser light is disclosed. However, the dry etching method can damage the device and affect the product characteristics. Besides, the dry etching method causes the wafer breakage and reduces the product yield.
In U.S. Pat. No. 6,849,524, a wet etching method of using a KOH cleaning solution to remove by-products generated from cutting the sapphire substrate by the laser light is disclosed. The cleaning solution can remove slag from the cutting and debris from the breaking. This method applies a protective coating on the cutting side of the sapphire wafer, and then cleans the sapphire wafer with the cleaning solution. However, the method cannot remove the slag completely and efficiently.
Therefore, how to remove the by-products resulting from the laser beam cutting efficiently to enhance the light extraction of LEDs becomes an important issue in the industry.